Organic thin-film transistor manufacturing method, organic thin-film transistor, and organic thin-film transistor sheet

ABSTRACT

An organic thin-film transistor is disclosed. The transistor may include a substrate, a gate electrode, a gate insulating layer, an organic semiconductor layer protective layer, a source electrode, and a drain electrode, wherein a layer formed on the organic semiconductor layer may have a light transmittance of not more than 10%.

CROSS REFERENCE TO RELATED APPLICATION

The present application is a continuation application under 35 U.S.C.§120 of U.S. patent application Ser. No. 11/074,287 filed on Mar. 7,2005, the entire contents of which are incorporated herein by reference.The 11/074,287 application is a divisional application under 35 U.S.C.§120 of U.S. patent application Ser. No. 10/742,194 filed on Dec. 19,2003, the entire contents of which are incorporated herein by reference.The 10/742,194 application claimed the benefit of the date of theearlier filed Japanese Patent Application No. JP 2002-376793 filed Dec.26, 2002. Priority to all of the above applications is claimed hereinalso.

FIELD OF THE INVENTION

The present invention relates to an organic thin-film transistormanufacturing method, an organic thin-film transistor manufactured bythe method, an organic thin-film transistor, and an organic thin-filmtransistor sheet.

BACKGROUND OF THE INVENTION

With the spread of information terminals, there are increasing demandsfor a flat panel display that serves as a display for a computer.Further, with development of the information technology, there has beenincreased a chance for information offered in a form of a sheet of papermedium in the past to be offered in an electronic form. An electronicpaper or a digital paper is demanded increasingly as a display mediumfor a mobile that is thin, lightweight and handy.

In the case of a display device of a flat sheet type, a display mediumis generally formed using an element that employs a liquid crystal,organic EL or electrophoresis method. In the display medium of thiskind, a technology for using an active driving element comprised of athin-film transistor (TFT), serving as an image driving element, is themain current for ensuring uniform image brightness and an imagerewriting speed.

The TFT is manufactured by a process comprising forming, on a glasssubstrate, a semiconductor layer of a-Si (amorphous silicone) or p-Si(poly-silicone) and metal films of source, drain and gate electrodes, inthe order. In the manufacture of a flat panel display employing such aTFT, a photolithography step with high precision is required in additionto a thin layer forming step requiring a vacuum line carrying out a CVDmethod or a sputtering method or a high temperature treatment step,which results in great increase of manufacturing cost or running cost.Recent demand for a large-sized display panel further increases thosecosts described above.

In order to overcome the above-described defects, an organic thin-filmtransistor employing an organic semiconducting material has beenextensively studied (refer to Japanese Patent O.P.I. Publication No.10-19000 and “Advanced Material”, 2002, No. 2, p. 99 (review)). Sincethe organic thin-film transistor can be manufactured at low temperatureemploying a lightweight substrate difficult to be broken, a flexibledisplay employing a resin film as a substrate can be realized (refer toSID '02 Digest P. 57). Further, employing an organic semiconductingmaterial allowing a wet process such as a printing method or a coatingmethod, a display manufacturing process can be realized which providesexcellent productivity and reduced cost.

However, an organic thin-film transistor, when allowed to stand in air,deteriorates, resulting in lowering of transistor properties. Further,an organic thin-film transistor, when manufactured by a processcomprising forming an organic semiconductor layer, followed by coatingof a light sensitive resin layer, and development of the light sensitiveresin layer air, results in deterioration of transistor properties dueto a solvent used for coating or components contained in a developerused for development.

An organic thin-film transistor employing a substrate such as a resinplate or a resin film is easily folded as compared with that employing aglass plate. Therefore, the former has problem in that properties as atransistor deteriorate due to folding, or due to light.

SUMMARY OF THE INVENTION

The present invention has been made in view of the above. An object ofthe invention is to provide an organic thin-film transistormanufacturing method minimizing deterioration during the manufacture oftransistor properties and minimizing deterioration with time or due tofolding of the transistor properties, and an organic thin-filmtransistor manufactured by the method. Another object of the inventionis to provide an organic thin-film transistor and an organic thin-filmtransistor sheet, each minimizing deterioration with time or due tofolding of the transistor properties.

BRIEF DESCRIPTION OF THE DRAWINGS

Brief Explanation of the Drawings

FIG. 1 is a structural example of the organic thin-film transistor ofthe invention (top gate type).

FIG. 2 is a structural example of the organic thin-film transistor ofthe invention (bottom gate type).

FIG. 3 is a schematic equivalent circuit diagram of one example of theorganic thin-film transistor sheet of the invention.

FIGS. 4(1) through 4(8) are illustrations for explaining one embodimentof the organic thin-film transistor manufacturing method of theinvention.

FIG. 5 is an illustration showing one structural example of acomparative organic thin-film transistor.

FIG. 6 is an illustration showing another structural example of acomparative organic thin-film transistor.

FIG. 7 is an illustration showing one structural example of an inventiveorganic thin-film transistor.

FIG. 8 is an illustration showing another structural example of aninventive organic thin-film transistor.

FIGS. 9(1) through 9(3) are illustrations for explaining anotherembodiment of the organic thin-film transistor manufacturing method ofthe invention.

FIG. 10 is an illustration of an inventive organic thin-film transistor.

DETAILED DESCRIPTION OF THE INVENTION

The above object of the invention can be attained by the followingconstitution.

An organic thin-film transistor may include a substrate, a gateelectrode formed on the substrate, a gate insulating layer formed on thesubstrate, an organic semiconductor protective layer with a through holeformed on the semiconductor layer, and a source electrode and a drainelectrode, each electrode being provided so as to contact the organicsemiconductor layer through the through hole, wherein a layer formed onthe organic semiconductor layer has a light transmittance of not morethan 10%.

Additionally, the organic semiconductor layer protective layer may beformed so as to contact the organic semiconductor layer.

Additionally, at least a part of the source electrode and at least apart of the drain electrode may exist in the through hole.

Additionally, the through hole may have a first hole and a second holeeach separated, the source electrode being provided so as to contact theorganic semiconductor layer through the first hole, and the drainelectrode being provided so as to contact the organic semiconductorlayer through the second hole.

Additionally, the organic semiconductor layer may have a lighttransmittance of not more than 10%.

Additionally, the organic semiconductor layer protective layer may beformed by coating an aqueous hydrophilic polymer solution or an aqueoushydrophilic polymer dispersion.

Additionally, the source electrode may be formed from a conductive pastecontaining metal particles, a conductive ink or a metal film precursor.

Additionally, the drain electrode may be formed from a conductive pastecontaining metal particles, a conductive ink or a metal film precursor.

Additionally, the source electrode may contain a conductive polymer.

Additionally the drain electrode may contain a conductive polymer.

Additionally, the substrate may comprise a resin.

Alternatively, an organic thin-film transistor may include a substrate,a subbing layer formed on the substrate, a gate electrode formed on thesubbing layer, a gate insulating layer formed on the subbing layer, anorganic semiconductor layer formed on the gate insulating layer, asource electrode formed on the organic semiconductor layer, a drainelectrode formed on the organic semiconductor layer, and an organicsemiconductor layer protective layer formed on the organic semiconductorlayer; wherein a layer formed on the organic semiconductor layer has alight transmittance of not more than 10%.

Alternatively, an organic thin-film transistor may include a substrate,a subbing layer formed on the substrate, an organic semiconductor layerformed on the subbing layer, a source electrode formed on the organicsemiconductor layer, a drain electrode formed on the organicsemiconductor layer, an organic semiconductor layer protective layerformed on the organic semiconductor layer, a gate insulating layerformed on the organic semiconductor layer protective layer and a gateelectrode formed on the gate insulating layer, wherein a layer formed onthe organic semiconductor layer has a light transmittance of not morethan 10%.

EMBODIMENT OF THE INVENTION

Embodiment of the invention will be explained below, employing Figures.

As the organic thin-film transistor of the invention, there are a topgate type transistor which comprises a substrate of a resin, an organicsemiconductor layer on the substrate, the organic semiconductor layercontacting a source electrode and a drain electrode, a gate insulatinglayer on the organic semiconductor layer, and a gate electrode on thegate insulating layer, and a bottom gate type transistor which comprisesa substrate of a resin, a gate electrode on the substrate, an organicsemiconductor layer on the substrate, the organic semiconductor layercontacting a source electrode and a drain electrode, a gate insulatinglayer on the organic semiconductor layer, and a gate electrode on thegate insulating layer.

The structural examples thereof will be shown in FIGS. 1 and 2.

FIG. 1 is a structural example of the top gate type transistor.

In FIG. 1, a subbing layer 2, containing a compound selected frompolymers, inorganic oxides, and inorganic nitrides, is provided on asubstrate 1 comprised of a resin. An organic semiconductor layer 6 isprovided on the subbing layer 2, and an organic semiconductor layerprotective layer 3 having through holes 30 is provided on the organicsemiconductor layer 6. A drain electrode 4 and a source electrode 5 areprovided so that both contact the organic semiconductor layer 6 throughthe through holes 30 of the organic semiconductor layer protective layer3. A gate insulating layer 7 is provided on the drain electrode 4,source electrode 5, and the organic semiconductor layer protective layer3, and a gate electrode 8 is provided on the gate insulating layer 7.

FIG. 2 is a structural example of the bottom gate type transistor.

In FIG. 2, a subbing layer 2, containing a compound selected frompolymers, inorganic oxides, and inorganic nitrides, is provided on asubstrate 1 comprised of a resin. A gate electrode 8 and a gateinsulating layer 7 are provided on the subbing layer 2. An organicsemiconductor layer 6 is provided on the gate insulating layer 7. Anorganic semiconductor layer protective layer 3 having through holes 30is provided on the organic semiconductor layer 6. A drain electrode 4and a source electrode 5 are provided so that both contact the organicsemiconductor layer 6 through the through holes 30 of the organicsemiconductor layer protective layer 3.

The organic thin-film transistor manufacturing method of the inventioncomprises the steps of a) forming a gate electrode on a substrate, b)forming a gate insulating layer on the substrate, c) forming an organicsemiconductor layer on the substrate, d) forming an organicsemiconductor layer protective layer on the organic semiconductor layer,e) removing a part of the organic semiconductor layer protective layer,and f) forming a source electrode and a drain electrode at portionswhere the organic semiconductor layer protective layer has been removed,so that the source electrode and drain electrode contacts the organicsemiconductor layer. In the above method, the order of the steps a), b)and c) is free. For example, after the steps c) through f) has beencarried out, the steps a) and b) are carried out.

The organic thin-film transistor of the invention comprises a substrate,a gate electrode on a substrate, a gate insulating layer formed on thesubstrate, an organic semiconductor layer formed on the substrate, anorganic semiconductor layer protective layer with a through hole formedon the organic semiconductor layer, a source electrode and a drainelectrode, each electrode being provided so as to contact the organicsemiconductor layer through the through hole. In the above organicthin-film transistor, the gate electrode may be located at the positionfarther from the substrate or at the position closer to the substratethan the source electrode and the drain electrode.

In the organic thin-film transistor of the invention, the organicsemiconductor layer protective layer preferably contacts the organicsemiconductor layer. Such an organic semiconductor layer protectivelayer, contacting the organic semiconductor layer, can preventdeterioration of the organic semiconductor layer due to air or a solventfor coating used in the manufacture, and can prevent deterioration ofperformance as a transistor. Further, the organic semiconductor layerprotective layer can provide excellent resistance to folding, wherebydeterioration due to folding of performance as a transistor can beminimized.

As a material of the organic semiconductor layer protective layer, amaterial is used which has no influence on the organic semiconductorlayer during or after manufacture of an organic thin-film transistor.When a light sensitive composition such as a light sensitive resin layeris coated on the organic semiconductor layer protective layer, amaterial is used which is not affected by the light sensitivecomposition during coating. Further, the material is preferred amaterial which is not affected during processing of the light sensitiveresin layer. Such a material is preferably a material containing ahydrophilic polymer, and more preferably an aqueous hydrophilic polymersolution or an aqueous hydrophilic polymer dispersion. The hydrophilicpolymer hereinafter referred to is a polymer soluble or dispersible inwater, an aqueous acidic or alkali solution, or an aqueous solution ofvarious surfactants. Examples of the hydrophilic polymer includepolyvinyl alcohol, a homopolymer or copolymer of HEMA, acrylic acid, oracryl amide. A material containing inorganic oxides or inorganicnitrides is also preferred, since it has no influence on the organicsemiconductor layer and is not influenced during coating of anotherlayer. Further, a material to be used in a gate insulating layerdescribed later can be also used. Preferred examples of the inorganicoxides include silicon oxide, aluminum oxide, tantalum oxide, titaniumoxide, tin oxide, vanadium oxide, barium strontium titanate, bariumzirconate titanate, zirconic acid lead carbonate, lead lanthanumtitanate, strontium titanate, barium titanate, barium magnesiumfluoride, bismuth titanate, strontium bismuth titanate, strontiumbismuth tantalate, bismuth niobate tantalate, and yttrium trioxide.Preferred examples of the inorganic nitrides include silicon nitride andaluminum nitride. The organic semiconductor layer protective layer inthe invention is preferably formed according to a coating method, andmore preferably formed by coating the aqueous hydrophilic polymersolution or the aqueous hydrophilic polymer dispersion.

The organic semiconductor layer protective layer containing inorganicoxides or inorganic nitrides is preferably formed according to anatmospheric pressure plasma method.

The plasma layer formation method at atmospheric pressure means a methodwherein a reactive gas is plasma-excited by discharge conducted atatmospheric pressure or at approximately atmospheric pressure, whereby athin-film is formed on a substrate. The method (hereinafter referred toalso as an atmospheric pressure plasma method) is described in JapanesePatent O.P.I. Publication Nos. 11-61406, 11-133205, 2000-121804,2000-147209, and 2000-185362. This method can form a thin film havinghigh performance at high productivity.

In the invention, the organic semiconductor layer protective layer has alight transmittance of preferably not more than 10%, and more preferablynot more than 1%. This can prevent deterioration due to light of theorganic semiconductor layer.

In the invention, light transmittance shows an average lighttransmittance of light having a wavelength capable of generating a lightgenerating carrier in the organic semiconductor layer. Generally, alight with a wavelength from 350 to 750 nm is preferably shielded.

In the invention, arrival of light at the organic semiconductor layershould be prevented in order to minimize deterioration due to light ofthe organic semiconductor layer. Accordingly, the light arrival may bereduced not only by the organic semiconductor layer protective layer butalso by another layer, provided on the organic semiconductor layer (alllayers in the case of multi-layers), each having a light transmittanceof not more than 10%, and more preferably not more than 1%. Thethickness of the organic semiconductor layer protective layer ispreferably 0.01 to 10 μm. This thickness range can provide a goodprotective property, and a source electrode and a drain electrode withgood resolution.

In order to reduce light transmittance of the layer, the layer cancontain colorants such as pigments and dyes, or UV absorbing agents.

The organic thin-film transistor of the invention comprises an organicsemiconductor layer protective layer having through holes which isprovided on an organic semiconductor layer, and a source electrode and adrain electrode both contacting the organic semiconductor layer throughthe through holes. The protective layer protects the organicsemiconductor layer during the manufacture of the organic thin-filmtransistor, and can minimize contact of the organic semiconductor layerwith air or a coating solvent during formation of the source and drainelectrodes, whereby deterioration of performance of the transistor canbe minimized.

The organic thin-film transistor of the invention comprises a subbinglayer containing a compound selected from inorganic oxides or inorganicnitrides or a subbing layer containing a polymer.

The inorganic oxides contained in the subbing layer include siliconoxide, aluminum oxide, tantalum oxide, titanium oxide, tin oxide,vanadium oxide, barium strontium titanate, barium zirconate titanate,zirconic acid lead carbonate, lead lanthanum titanate, strontiumtitanate, barium titanate, barium magnesium fluoride, bismuth titanate,strontium bismuth titanate, strontium bismuth tantalate, bismuth niobatetantalate, and yttrium trioxide. The inorganic nitrides include siliconnitride and aluminum nitride.

Of these, silicon oxide, aluminum oxide, tantalum oxide, titanium oxideor silicon nitride is preferred.

In the invention, the subbing layer containing a compound selected frominorganic oxides or inorganic nitrides is preferably formed according tothe atmospheric pressure plasma method described above.

Examples of the polymer used in the subbing layer include a polyesterresin, a polycarbonate resin, a cellulose resin, an acryl resin, apolyurethane resin, a polyethylene resin, a polypropylene resin, apolystyrene resin, a phenoxy resin, a norbornene resin, an epoxy resin,vinyl chloride-vinyl acetate copolymer, a vinyl chloride resin, vinylacetate-vinyl alcohol copolymer, a partially saponificated vinylchloride-vinyl acetate copolymer, vinyl chloride-vinylidene chloridecopolymer, vinyl chloride-acrylonitrile copolymer, ethylene-vinylalcohol copolymer, polyvinyl alcohol, chlorinated polyvinyl chloride,ethylene-vinyl chloride copolymer, ethylene-vinyl acetate copolymer, apolyamide resin, an ethylene-butadiene resin, a butadiene-acrylonitrileresin, a silicone resin, and a fluorine-contained resin.

As organic semi-conductive materials for the organic semiconductor layerof the organic thin-film transistor of the invention, π-conjugatedmaterials are used. Examples of the π-conjugated materials includepolypyrroles such as polypyrrole, poly(N-substituted pyrrole),poly(3-substituted pyrrole), and poly(3,4-disubstituted pyrrole);polythiophenes such as polythiophene, poly(3-substituted thiophene),poly(3,4-disubstituted thiophene), and polybenzothiophene;polyisothianaphthenes such as polyisothianaphthene;polythienylenevinylenes such as polythienylenevinylene;poly(p-phenylenevinylenes) such as poly(p-phenylenevinylene);polyanilines such as polyaniline, poly(N-substituted aniline),poly(3-substituted aniline), and poly(2,3-substituted aniline);polyacetylnenes such as polyacetylene; polydiacetylens such aspolydiacetylene; polyazulenes such as polyazulene; polypyrenes such aspolypyrene; polycarbazoles such as polycarbazole and poly(N-substitutedcarbazole), polyselenophenes such as polyselenophene; polyfurans such aspolyfuran and polybenzofuran; poly(p-phenylenes) such aspoly(p-phenylene); polyindoles such as polyindole; polypyridazines suchas polypyridazine; polyacenes such as naphthacene, pentacene, hexacene,heptacene, dibenzopentacene, tertabenzopentacene, pyrene, dibenzopyrene,chrysene, perylene, coronene, terylene, ovalene, quoterylene, andcircumanthracene; derivatives (such as triphenodioxazine,triphenodithiazine, hexacene-6,15-quinone) in which some of carbon atomsof polyacenes are substituted with atoms such as N, S, and O or with afunctional group such as a carbonyl group; polymers such as polyvinylcarbazoles, polyphenylene sulfide, and polyvinylene sulfide; andpolycyclic condensation products described in Japanese Patent O.P.I.Publication No. 11-195790.

Further, oligomers having repeating units in the same manner as in theabove polymers, for example, thiophene hexamers includingα-sexithiophene, α, ω-dihexyl-α-sexithiophene,α,ω-dihexyl-α-quiinquethiophene, andα,ω-bis(3-butoxypropyl)-α-sexithiophene, or styrylbenzene derivatives,can be suitably employed.

Further, listed are metallophthalocyanines such as copperphthalocyanine, and fluorine-substituted copper phthalocyaninesdescribed in Japanese Patent O.P.I. Publication No. 11-251601;tetracarboxylic acid diimides of condensed ring compounds includingnaphthalene tetracarboxylic acid imides such as naphthalene1,4,5,8-teracarboxylic acid diimide,N,N′-bis(4-trifluoromethylbenzyl)naphthalene 1,4,5,8-tretracarboxylicacid diimide, N,N′-bis(1H,1H-perfluoroctyl)naphthalene1,4,5,8-tetracarboxylic acid diimide derivatives,N,N′-bis(1H,1H-perfluorobutyl)naphthalene 1,4,5,8-tetracarboxylic aciddiimide derivatives, N,N′-dioctylnaphthalene 1,4,5,8-tetracarboxylicacid diimide derivatives, and naphthalene 2,3,6,7-tetracarboxylic aciddiimides, and anthracene tetracarbocylic acid diimides such asanthracene 2,3,6,7-tetracarboxylic acid diimides; fullerenes such asC₆₀, C₇₀, C₇₆, C₇₈, and C₈₄; carbon nanotubes such as SWNT; and dyessuch as merocyanines and hemicyanines.

Of these π conjugated compounds, preferably employed is at least oneselected from the group consisting of oligomers which have thiophene,vinylene, thienylenevinylene, phenylenevinylene, p-phenylene, theirsubstitution product or at least two kinds thereof as a repeating unitand have a repeating unit number n of from 4 to 10, polymers which havethe same unit as above and a repeating unit number n of at least 20,condensed polycyclic aromatic compounds such as pentacene, fullerenes,condensed cyclic tetracarboxylic acid diimides of condensed ringcompounds, and metallo-phthalocyanines.

Further, employed as other materials for organic semiconductors may beorganic molecular complexes such as a tetrathiafulvalene(TTF)-tetracyanoquinodimethane (TCNQ) complex, abisethylenetetrathiafulvalene (BEDTTTF)-perchloric acid complex, aBEDTTTF-iodine complex, and a TCNQ-iodine complex. Still further,employed may be a conjugated polymers such as polysilane andpolygermane, as well as organic-inorganic composite materials describedin Japanese Patent O.P.I. Publication No. 2000-260999.

In the invention, the organic semiconductor layer may be subjected to aso-called doping treatment (referred to also as simply doping) byincorporating in the layer, materials working as an acceptor whichaccepts electrons, for example, acrylic acid, acetamide, materialshaving a functional group such as a dimethylamino group, a cyano group,a carboxyl group and a nitro group, benzoquinone derivatives, ortetracyanoethylene, tetracyanoquinodimethane or their derivatives, ormaterials working as a donor which donates electrons, for example,materials having a functional group such as an amino group, a triphenylgroup, an alkyl group, a hydroxyl group, an alkoxy group, and a phenylgroup; substituted amines such as phenylenediamine; anthracene,benzoanthracene, substituted benzoanthracenes, pyrene, substitutedpyrene, carbazole and its derivatives, and tetrathiafulvalene and itsderivatives.

The doping herein means that an electron accepting molecule (acceptor)or an electron donating molecule (donor) is incorporated in the organicsemiconductor layer as a dopant. Accordingly, the layer, which has beensubjected to doping, is one which comprises the condensed polycyclicaromatic compounds and the dopant. Employed as the dopant used in thepresent invention may be either acceptor or donor.

The methods for forming the organic semiconductor layer include a vacuumdeposition method, a molecular beam epitaxial growth method, an ioncluster beam method, a low energy ion beam method, an ion platingmethod, a CVD method, a sputtering method, a plasma polymerizationmethod, an electrolytic polymerization method, a chemical polymerizationmethod, a spray coating method, a spin coating method, a blade coatingmethod, a dip coating method, a casting method, a roll coating method,an bar coating method, a die coating method, and an LB method. Thesemethods may be used according to kinds of materials used. However, ofthese, a spin coating method, a blade coating method, a dip coatingmethod, a roll coating method, a bar coating method, and a die coatingmethod are preferred from the viewpoint of productive efficiency.

When a precursor such as pentacene is soluble in a solvent as disclosedin Advanced Material 1999, Vol. 6, p. 480-483, a precursor layer formedby coating of the precursor solution may be heat treated to form anintended organic material layer.

The thickness of the organic semiconductor layer is not specificallylimited. The thickness of an organic semiconductor layer comprised ofthe organic semiconductor materials often has a great influence onproperties of the resultant transistor. Accordingly, the thickness ofthe layer differs due to kinds of the organic semiconductor materialsused, but it is ordinarily not more than 1 μm, and preferably from 10 to300 nm.

In the organic thin-film transistor of the invention, materials forconstituting a gate electrode, a source electrode, and a drain electrodeare not particularly restricted as long as they are electricallyconductive materials. Employed as the materials are platinum, gold,silver, nickel, chromium, copper, iron, tin, antimony, lead, tantalum,indium, palladium, tellurium, rhenium, iridium, aluminum, ruthenium,germanium, molybdenum, tungsten, tin oxide-antimony, indium oxide-tin(ITO), fluorine-doped zinc oxide, zinc, carbon, graphite, glassy carbon,silver paste as well as carbon paste, lithium, beryllium, sodium,magnesium, potassium, calcium, scandium, titanium, manganese, zirconium,gallium, niobium, sodium, sodium-potassium alloy, magnesium, lithium,aluminum, magnesium/copper mixtures, magnesium/silver mixtures,magnesium/aluminum mixtures, magnesium/indium mixtures,aluminum/aluminum oxide mixtures, and lithium/aluminum mixtures. Asmaterials for the above electrodes, electrically conductive polymersknown in the art, which increase electrical conductivity upon beingdoped, are preferably employed. Examples thereof include electricallyconductive polyaniline, electrically conductive polypyrrole,electrically conductive polythiophene, and a complex ofpolyethylenedioxythiophene and polystyrene sulfonic acid. The source anddrain electrodes are those providing less electrical resistance at aninterface between the electrodes and the semiconductor layer, and arepreferably electrodes comprised of a conductive polymer, platinum, gold,silver, or ITO in p-type semiconductor.

In the invention, the source electrode and drain electrode arepreferably electrodes formed from a flowable electrode material such asa solution, paste, ink, or a dispersion solution containing the aboveelectrically conductive material, and more preferably electrodes formedfrom a flowable electrode material containing a conductive polymer,platinum, gold, silver, or copper. As a solvent or a dispersion medium,a solvent or dispersion medium containing water in an amount of not lessthan 60%, and more preferably not less than 90% is preferred in thatdamage to the organic semiconductor is reduced.

As a metal particle-containing flowable electrode material, a knownconductive paste can be used. The metal particle-containing dispersionis preferably a dispersion in which metal particles with a particle sizeof from 1 to 50 nm, and preferably from 1 to 10 nm, and optionally adispersion stabilizer are dispersed in water or an appropriate solvent.

Materials for the metal particles include platinum, gold, silver,nickel, chromium, copper, iron, tin, antimony, lead, tantalum, indium,palladium, tellurium, rhenium, iridium, aluminum, ruthenium, germanium,molybdenum, tungsten, and zinc.

An electrode is preferably formed from a metal particle dispersion inwhich metal particles of these metals are dispersed in a dispersionmedium such as water or an organic solvent in the presence of an organicdispersion stabilizer

Methods for preparing such a metal particle dispersion include aphysical preparation method such as a gas vaporization method, asputtering method, or a metallic vapor preparation method and a chemicalpreparation method such as a colloid method or a co-precipitation methodin which metal ions are reduced in a liquid phase to produce metalparticles. The metal particles dispersion are preferably ones preparedaccording to a colloid method disclosed in Japanese Patent O.P.I.Publication Nos. 11-76800, 11-80647, 11-319538, and 2000-239853, or onesprepared according to a gas vaporization method disclosed in JapanesePatent O.P.I. Publication Nos. 2001-254185, 2001-53028, 2001-35814,2001-35255, 2001-124157 and 2000-123634. An electrode pattern is formedfrom these metal particle dispersions dried, and optionally subjected toheat treatment at from 100 to 300° C., and preferably from 150 to 200°C., whereby the metal particles are heat-fused to form an electrode inan intended form.

Methods for forming the electrode include a method in which aphotolithographic method or a lift-off method, known in the art, isapplied to an electrically conductive layer of the materials describedabove, which has been formed employing a vacuum deposition method or asputtering method, and a method in which a resist layer is subjected toetching which has been prepared employing thermal transfer or ink jetprinting onto a foil of metal such as aluminum or copper. Further, anelectrically conductive polymer solution or dispersion, or a minuteelectrically conductive particle dispersion may be subjected directly topatterning, employing ink jet printing to obtain an electrode. Anelectrode may also be formed in such a manner that a coated layer issubjected to lithography or laser ablation. In addition, a method mayalso be employed in which ink comprising either an electricallyconductive polymer or minute electrically conductive particles, orelectrically conductive paste is subjected to patterning, employing anyof the printing methods such as letter press, intaglio printing,lithography, or screen printing.

In the organic thin-film transistor of the invention, the source anddrain electrodes are preferably formed according to photolithography,wherein a light sensitive resin solution is coated on the entire surfaceof the organic semiconductor layer protective layer to form a lightsensitive resin layer.

As a material for the light sensitive resin layer, a well-known positiveworking or negative working material can be used, but a laser sensitivematerial is preferably used. As such a material for the photoresist,there are (1) a dye sensitized photo-polymerizable light-sensitivematerial disclosed in Japanese Patent O.P.I. Publication Nos. 11-271969,2001-117219, 11-311859, and 11-352691, (2) an infrared laser-sensitivenegative working material disclosed in Japanese Patent O.P.I.Publication No. 9-179292, U.S. Pat. No. 5,340,699, and Japanese PatentO.P.I. Publication Nos. 10-90885, 2000-321780, and 2001-154374, and (3)an infrared laser-sensitive positive working material in Japanese PatentO.P.I. Publication Nos. 9-171254, 5-115144, 10-87733, 9-43847,10-268512, 11-194504, 11-223936, 11-84675, 11-174681, 7-282575, and2000-56452, WO97/39894, and WO98/42507. The material of item (2) or (3)above is preferred in that its use is not limited to use in the dark.

In the photolithography, after the above, an electrode pattern is formedfrom a metal particle dispersion or an electrically conductive polymeras a material for the source and drain, and optionally heat fused,whereby the source or drain electrode can be easily and preciselyformed. The above method can easily form various shapes, which makes itpossible to easily produce an organic thin-film transistor.

Solvents for preparing a coating liquid of the light sensitive resinlayer include propylene glycol monomethyl ether, propylene glycolmonoethyl ether, methyl cellosolve, methyl cellosolve acetate, ethylcellosolve, ethyl cellosolve acetate, dimethylformamide,dimethylsulfoxide, dioxane, acetone, cyclohexanone, trichloroethylene,and methyl ethyl ketone. These solvents may be used singly or as amixture of two or more kinds thereof.

As a method for forming a light sensitive resin layer, there is acoating method such as a spray coating method, a spin coating method, ablade coating method, a dip coating method, a casting method, a rollcoating method, a bar coating method or a die coating method.

In order to restrain arrival of light at the organic semiconductor layerto minimize deterioration due to light of the organic semiconductorlayer, light transmittance of the light sensitive resin layer may bereduced by addition of colorants such as dyes or a UV absorbing agent,wherein light transmittance of the light sensitive resin layer ispreferably not more than 10%, and more preferably not more than 1%.

The formed light sensitive resin layer is imagewise exposed. As a lightsource for the imagewise exposure, there are an argon laser, asemi-conductive laser, a He—Ne laser, a YAG laser, and a carbon dioxidegas laser, and a semi-conductive laser, which has an emission wavelengthat the infrared wavelength regions, is preferred. The output power ofthe laser is suitably not less than 50 mW, and preferably not less than100 mW.

Subsequently, the exposed light sensitive resin layer is subjected todevelopment.

The developing solution for development of the light sensitive resinlayer is suitably an aqueous alkali developing solution. Examples of theaqueous alkali developing solution include an aqueous solution of analkali metal salt such as sodium hydroxide, potassium hydroxide, sodiumcarbonate, potassium carbonate, sodium metasilicate, potassiummetasilicate, sodium secondary phosphate, or sodium tertiary phosphate,and an aqueous solution of an alkali compound such as ammonia,ethylamine, n-propylamine, diethylamine, di-n-propylamine,triethylamine, methyldiethylamine, dimethylethanolamine,triethanolamine, tetramethylammonium hydroxide, tetraethylammoniumhydroxide, choline, pyrrole, piperidine,1,3-diazabicyclo-[5,4,0]-7-undecane or1,5-diazabicyclo-[4,3,0]-5-nonane. In the invention, the concentrationof the alkali metal salt or the alkali compound in the aqueous alkalideveloping solution is ordinarily from 1 to 10% by weight, andpreferably from 2 to 5% by weight.

The developing solution may optionally contain an anionic surfactant, anamphoteric surfactant or an organic solvent such as alcohol. Examples ofthe organic solvent include propylene glycol, ethylene glycol monophenylether, benzyl alcohol and n-propyl alcohol.

The step of removing the light sensitive resin layer may be optionallyadded. In the case where the residual light sensitive resin layer isremoved after an electrode pattern is formed from the metal particledispersion or the electrically conductive polymer, the light sensitiveresin composition used is preferably a positive working one. Thecomposition for forming the light sensitive resin layer preferablycontains a phenol resin such as novolak resin or polyvinyl phenol.Examples of the novolak resin include phenol-formaldehyde resin,cresol-formaldehyde resin, phenol-cresol-formaldehyde cocondensationresin disclosed in Japanese Patent O.P.I. Publication No. 55-57841, anda cocondensation resin of p-substituted phenol and phenol or cresol withformaldehyde disclosed in Japanese Patent O.P.I. Publication No.55-127553. When the residual light sensitive resin layer is removedafter an electrode pattern is formed from the metal particle dispersionor the electrically conductive polymer, the removing solvent is selectedfrom the organic solvents such as an alcohol solvent, an ether solvent,an ester solvent, a ketone solvent, and a glycol ether solvent, whichare used for preparing a coating liquid of the light-sensitive resinlayer. The ether or ketone solvent is preferred in order to minimize aninfluence on the electrically conductive polymer layer, i.e., in orderto minimize reduction of electric conductivity or increase a residualamount of the electrically conductive polymer layer. The ether solventsuch as tetrahydrofuran (THF) is most preferred.

In the invention, an ablation layer can be used to form electrodes. Theablation layer in the invention contains an actinic light absorbingagent, a binder resin, and optionally various additives.

As the actinic light absorbing agent, there are various organic orinorganic materials capable of absorbing actinic light. For example,when infrared laser is used as actinic light, pigment absorbing infraredlight, dyes, metals, metal oxides, metal nitrides, metal carbonates,metal borides, graphite, carbon black, titanium black, and ferromagneticmetal powder such as metal magnetic powder containing Al, Fe, Ni, or Coas a main component can be used. Among these, carbon black, dyes such ascyanine dyes and Fe containing ferromagnetic metal powder are preferred.The content of the actinic light absorbing agent in the ablation layeris from 30 to 95% by weight, and preferably from 40 to 80% by weight.

The binder resin used in the invention may be any resin as long as itcan carry the actinic light absorbing agent described above. Examples ofthe binder resin include a polyurethane resin, a polyester resin, avinyl chloride resin, a polyvinyl acetal resin, a cellulose resin, anacryl resin, a phenoxy resin, a polycarbonate resin, a polyamide resin,a phenol resin, and an epoxy resin. The content of the binder resin inthe ablation layer is from 5 to 70% by weight, and preferably from 20 to60% by weight.

In the invention, the ablation layer refers to a layer to be ablated byirradiation of a high density energy light. Herein, “ablated” refers tophenomenon in which an ablation layer is completely scattered or a partof the layer is destroyed and/or scattered by its physical or chemicalchange, or the physical or chemical change occurs only near theinterface between the layer and its adjacent layer. In the invention, aresist can be formed employing this phenomenon, and then electrodes canbe formed.

The high density energy light can be used without any special limitationas long as it is light capable of ablating an ablation layer onexposure. As an exposure method, flash exposure may be carried outthrough a photomask employing a xenon lamp, a halogen lamp or a mercurylamp, or scanning exposure may be carried out employing a convergentlaser light. Infrared laser, particularly a semiconductor laser havingan output power of from 20 to 200 mW per one beam is preferably used.The energy density used is preferably from 50 to 500 mJ/cm², and morepreferably from 100 to 300 mJ/cm².

Various insulating layers may be employed as the gate insulating layerof the organic thin-film transistor of the invention. The insulatinglayer is preferably an inorganic oxide layer comprised of an inorganicoxide with high dielectric constant. Examples of the inorganic oxideinclude silicon oxide, aluminum oxide, tantalum oxide, titanium oxide,tin oxide, vanadium oxide, barium strontium titanate, barium zirconatetitanate, zirconic acid lead carbonate, lead lanthanum titanate,strontium titanate, barium titanate, barium magnesium fluoride, bismuthtitanate, strontium bismuth titanate, strontium bismuth tantalate,bismuth niobate tantalate, and yttrium trioxide. Of these, siliconoxide, silicon nitride, aluminum oxide, tantalum oxide or titanium oxideis particularly preferred. An inorganic nitride such as silicon nitrideor aluminum nitride can be also suitably used.

The methods for forming the above layer include a dry process such as avacuum deposition method, a molecular beam epitaxial growth method, anion cluster beam method, a low energy ion beam method, an ion platingmethod, a CVD method, a sputtering method, or an atmospheric pressureplasma method, a wet process such as a spray coating method, a spincoating method, a blade coating method, a dip coating method, a castingmethod, a roll coating method, an bar coating method, or a die coatingmethod, and a patterning method such as a printing method or an ink-jetmethod. These methods can be used due to kinds of materials used in theinsulating layer.

As the typical wet process can be used a method of coating a dispersionliquid and drying, the liquid being obtained by dispersing inorganicoxide particles in an organic solvent or water optionally in thepresence of a dispersant such as a surfactant, or a so-called sol gelmethod of coating a solution of an oxide precursor such as an alkoxideand drying.

Among the above, the preferred is an atmospheric pressure plasma method.

It is preferred that the gate insulating layer is comprised of ananodization film or an anodization film and an insulating film. Theanodization film is preferably subjected to sealing treatment. Theanodization film is formed on a metal capable of being anodized byanodizing the metal according to a known method.

Examples of the metal capable of being anodized include aluminum andtantalum. An anodization treatment method is mot specifically limitedand the known anodization treatment method can be used. Anodizationtreatment forms an anodization film. An electrolytic solution used inthe anodization treatment may be any as long as it can form a porousoxidation film. Examples of electrolytes in the electrolytic solutioninclude sulfuric acid, phosphoric acid, oxalic acid, chromic acid, boricacid, sulfamic acid, benzene sulfonic acid or their salt, and a mixturethereof. Anodization treatment conditions cannot be specified since theyvary due to kinds of an electrolytic solution used. Generally, theconcentration of the electrolytic solution is from 1 to 80% by weight,temperature of the electrolytic solution is from 5 to 70 C, electriccurrent density is from 0.5 to 60 A/dm2, voltage applied is from 1 to100 V, and electrolytic time is from 10 seconds to 5 minutes. It ispreferred that an aqueous solution of sulfuric acid, phosphoric acid orboric acid is used as an electrolytic solution, and direct current isused. Alternating current can be also used. Anodization treatment ispreferably carried out at an electric current density of from 0.5 to 20A/dm2 at an electrolytic solution temperature of from 20 to 50 for 20 to250 seconds.

Examples of the organic compound used in an organic compound layerinclude polyimide, polyamide, polyester, polyacrylate, a photo-curableresin such as a photo-radical polymerizable or photo-cationpolymerizable resin, a copolymer containing an acrylonitrile unit,polyvinyl phenol, polyvinyl alcohol, novolak resin, andcyanoethylpullulan.

As a method of forming the organic compound layer, the wet processdescribed above is preferably used.

An inorganic oxide layer and an organic oxide layer can be used incombination and superposed. The thickness of the insulating layer isgenerally 50 nm to 3 μm, and preferably from 100 nm to 1 μm.

An orientation layer may be provided between the gate insulating layerand the organic semiconductor layer. As the orientation layer, a selforganization layer is preferably used which is formed from a silanecoupling agent such as octadecyltrichlorosilane ortrichloromethylsilane, alkane phosphoric acid, alkane sulfonic acid, oran alkane carboxylic acid.

In the invention, the substrate is comprised of a resin, and forexample, it is possible to use a plastic film sheet. Examples of theplastic film include films comprised of, for example, polyethyleneterephthalate (PET), polyethylene naphthalate (PEN), polyethersulfone(PES), polyetherimide, polyether ether ketone, polyphenylene sulfide,polyallylate, polyimide, polycarbonate (PC), cellulose triacetate (TAC),or cellulose acetate propionate (CAP). Use of the plastic film makes itpossible to decrease weight, to enhance portability, and to enhancedurability against impact due to its flexibility, as compared to glass.

In the invention, a transistor protective layer can be provided on theorganic thin-film transistor of the invention. Materials for thetransistor protective layer include inorganic oxides or nitridesdescribed above, and the transistor protective layer is preferablyformed according to the atmospheric pressure plasma method, wherebyresistance of the organic thin-film transistor is improved.

Next, the manufacturing method of the organic thin-film transistor ofthe invention will be explained.

The manufacturing method of the organic thin-film transistor of theinvention comprising a substrate comprised of a resin and providedthereon, a gate electrode, a gate insulating layer, an organicsemiconductor layer, an organic semiconductor layer protective layer, asource electrode and a drain electrode, the method comprising the stepsof forming a gate electrode; forming a gate insulating layer; forming anorganic semiconductor layer; forming an organic semiconductor layerprotective layer so that the organic semiconductor layer protectivelayer contacts the resulting organic semiconductor layer; forming asource layer; and forming a drain electrode, wherein the organicsemiconductor layer protective layer is removed at portions to form thesource and drain electrodes to reveal the organic semiconductor layer atthe portions, and then the source and drain electrodes are formed on therevealed organic semiconductor layer. Employing the above method, theorganic thin-film transistor is protected immediately after itsformation by the organic semiconductor layer protective layer, which canprevent deterioration of the organic semiconductor layer due to air or asolvent for coating used in the manufacture, and can preventdeterioration of performance of the transistor. Further, the organicsemiconductor layer protective layer can provide excellent resistance tofolding, whereby deterioration due to folding of performance of thetransistor can be minimized. Further, during formation of the source anddrain electrodes, deterioration of the organic semiconductor layer dueto air or a solvent for coating used in the manufacture can beprevented, minimizing deterioration of performance of the transistor.

In the manufacturing method of the invention of the organic thin-filmtransistor, a source electrode and a drain electrode are preferablyformed according to photolithography as described above. Thephotolithography process comprises the steps of forming a lightsensitive resin layer so that the light sensitive resin layer contactsan organic semiconductor layer protective layer, exposing the resultinglight sensitive resin layer, developing the exposed light sensitiveresin layer, removing, during or after the developing step, the organicsemiconductor layer protective layer at portions to form the source anddrain electrodes to reveal the organic semiconductor layer at theportions, and then forming a source electrode and a drain electrode.Even if the organic thin-film transistor of the invention ismanufactured through formation of a light sensitive resin layer,exposure and development described above, deterioration of the organicsemiconductor layer is minimized, since the organic thin-film transistorhas an organic semiconductor layer protective layer. Further, since theorganic semiconductor layer protective layer at portions to form asource electrode and a drain electrode is removed just before the sourceelectrode and drain electrode are formed at the portions, deteriorationof transistor characteristics of the organic semiconductor layer isminimized.

FIG. 3 shows an equivalent circuit diagram of one embodiment of theorganic thin-film transistor sheet 10 of the invention, in which pluralorganic thin-film transistors of the invention are arranged.

The organic thin-film transistor sheet 10 comprises organic thin-filmtransistors 14 arranged in a matrix form. Numerical number 11 is a gatebusline of the gate electrode of each of the organic thin-filmtransistors 14, and numerical number 12 a source busline of the sourceelectrode of each of the organic thin-film transistors 14. Outputelement 16 is connected to the drain electrode of each of the organicthin-film transistors 14. The output element 16 is for example, a liquidcrystal or an electrophoresis element, which constitutes pixels in adisplay. In FIG. 3, liquid crystal as the output element 16 is shown inan equivalent circuit diagram comprised of a capacitor and a resistor.Numerical number 15 shows a storage capacitor, numerical number 17 avertical drive circuit, and numerical number 18 a horizontal drivecircuit.

The method of the invention can provide an organic thin-film transistorsheet, in which organic thin-film transistors are arrangedtwo-dimensionally on a flexible resin, having strong adhesion betweenthe substrate and the TFT constitution layer, excellent mechanicalstrength, and strong resistance to folding of the substrate.

EXAMPLES

Next, the present invention will be explained employing examples, but isnot limited thereto.

Example 1 Preparation of Organic Thin-Film Transistor Samples 1 through9

(1) Preparation of Organic Thin-Film Transistor Sample 1

<Preparation of Substrate>

A mixture of 3.04 g (20 mmol) of tetramethoxysilane, 1.52 g of methylenechloride, and 1.52 g of ethanol was mixed with 0.72 g of an aqueous 0.5%by weight nitric acid solution for hydrolysis, and stirred at roomtemperature for one hour. A solution in which 1.60 g ofdiacetylcellulose L50 (produced by Daicel Co., Ltd.) was dissolved in amixed solvent of 5.3 g of ethanol and 60.9 g of methyl acetate was addedto the resulting mixture above, and stirred for one hour to obtain adope. The resulting dope was cast on a moving gum belt through a doctorblade with a gap width of 800 μm, and dried at 120° C. for 30 minutes toobtain a substrate 1 with a thickness of 200 μm. The substrate 1 had aTg of 226° C., which was obtained by dynamic viscoelastic measurement.

The surface of substrate 1 was corona discharged at 50 W/m²/min and thencoated with a coating liquid having the following composition to obtaina layer of a dry thickness of 2 μm. The resulting layer was dried at 50°C. for 5 minutes, and hardened by being exposed for 4 seconds employinga 60 W/cm high pressure mercury lamp 10 cm distant from the layer.Dipentaerythritol hexacrylate monomer 60 g Dipentaerythritol hexacrylatedimmer 20 g Dipentaerythritol hexacrylate trimer 20 g or polymer higherthan the trimer Diethoxybenzophenone  2 g (UV-intiator)Silicon-containing surfactant  1 g Methyl ethyl ketone 75 g Methylpropylene glycol 75 g

The resulting hardened layer was subjected to continuous atmosphericpressure plasma treatment under the following condition to give a 50 nmthick silicon oxide layer on the hardened layer. This layer was asubbing layer 2. (Gas used) Inert gas: Helium 98.25% by volume Reactivegas 1: an oxygen gas  1.5% by volume Reactive gas 2: tetraethoxysilanevapor  0.25% by volume (bubbled with a helium gas) (Condition ofdischarge) Discharge output power:      10 W/cm²(Condition of Electrodes)

Electrodes used were prepared as follows:

A stainless steel jacket roll base material having a cooling device (notillustrated in FIG. 2) employing chilled water was coated with analumina thermal spray layer. After that, a solution prepared by dilutingtetramethoxysilane with ethyl acetate was coated on the resultingelectrode, dried, hardened by UV ray irradiation to carry out sealingtreatment, and smoothed to give an dielectric layer (dielectricconstant: 10) with an Rmax of 5 μm on the surface of the material. Thus,a roll electrode was obtained. Further, a hollow prismatic stainlesssteel pipe was processed in the same manner as above to obtain a hollowprismatic electrode as a voltage application electrode. The rollelectrode was grounded.

<Formation of Gate Electrode> (FIG. 4(1))

A light sensitive resin layer 1 having the following composition wascoated on the subbing layer 2 above, and dried at 100° C. for 1 minuteto form a light sensitive resin layer (not illustrated) with a thicknessof 2 μm. (Light sensitive resin layer 1) Dye A 7 parts Novolak resin 90parts (Condensation product of phenol, m-, p-mixed cresol, andformaldehyde, Mw = 4,000, phenol:m-cresol:p-cresol = 5:57:38 by mole)Crystal violet 3 parts Propylene glycol monomethyl ether 1000 partsDye A

The light sensitive resin layer was exposed at an energy density of 200mJ/cm² employing a 100 mW semiconductor laser emitting 830 nm light togive a gate busline pattern and a gate electrode pattern, and developedwith an alkali developing solution to form a resist.

A 300 nm thick aluminum layer was formed on the entire surface of thedeveloped material according to a sputtering method, and the resist wasremoved with MEK to obtain a gate busline and a gate electrode 8.

<Formation of Anodization Film> (FIG. 4(1))

The resulting material was sufficiently washed, and anodized in anaqueous 30% by weight sulfuric acid solution by supplying direct currentfor 2 minutes through a 30V low voltage power source to give ananodization film 9 with a thickness of 120 nm. The resulting layer wassufficiently washed, and subjected to vapor sealing treatment in a vaporsaturated chamber at 1000C.

<Formation of Gate Insulating Layer> (FIG. 4(2))

The resulting layer was subjected to atmospheric pressure plasmadischarge treatment at 200° C. to obtain a 30 μm thick titanium oxidelayer a gate insulating layer 7 in the same manner as above, except thatthe following gas was used. (Gas used) Inert gas: Argon 98.9% by volumeReactive gas 1: a hydrogen gas  0.8% by volume Reactive gas 2:tetrapropoxytitanium vapor  0.3% by volume (bubbled at 150° C. withargon helium gas)<Formation of Organic Semiconductor Layer> (FIG. 4(3))

A chloroform solution of Compound C described later was ejected ontoportions of the gate insulating layer where channel was to be formed,employing a piezo type ink jet printer, dried at 50° C. for 3 minutes,and heated at 200° C. for 10 minutes to obtain an organic semiconductorlayer 6 of a 50 nm thick pentacene film.Compound C

<Formation of Organic Semiconductor Layer Protective Layer> (FIG. 4(4))

An aqueous polyvinyl alcohol solution, in which purified polyvinylalcohol was dissolved in water sufficiently purified employing a superpure water manufacturing apparatus, was coated on the organicsemiconductor layer 6, and dried at 100° C. in a nitrogen atmosphere toobtain an organic semiconductor layer protective layer 3 of polyvinylalcohol with a thickness of 1 μm.

<Formation of Light Sensitive Resin Layer> (FIG. 4(5))

A light sensitive resin layer 1 having the following composition wascoated on the organic semiconductor layer protective layer above, anddried at 100° C. for 1 minute to form a light sensitive resin layer 19with a thickness of 2 μm. (Light sensitive resin layer 1) Dye A 7 partsNovolak resin 90 parts (Condensation product of phenol, m-, p-mixedcresol, and formaldehyde, Mw = 4,000, phenol:m-cresol:p-cresol = 5:57:38by mole) Crystal violet 3 parts Propylene glycol monomethyl ether 1000parts<Exposure and Development of Light Sensitive Resin Layer> (FIG. 4(6))

The light sensitive resin layer 19 was exposed at an energy density of200 mJ/cm² employing a 100 mW semiconductor laser emitting 830 nm lightto give a source electrode pattern and a drain electrode pattern, anddeveloped with an alkali developing solution to form a resist 19′.

<Removal of Organic Semiconductor Layer Protective Layer> (FIG. 4(6))

The resulting material was sufficiently washed with water to remove thepolyvinyl alcohol protective layer at portions other than the resist19′.

<Formation of Source Electrode and Drain Electrode> (FIGS. 4(7) and4(8))

An aqueous dispersion (BAYTRON P produced by Bayer Co., Ltd.) ofpolystyrene sulfonic acid and poly(ethylenedioxy-thiophene) was coatedon the entire surface of the resulting material, and dried at 100° C. toform a layer comprised of polystyrene sulfonic acid andpoly(ethylenedioxythiophene). Further, an aqueous Ag particle dispersionas disclosed in Japanese Patent O.P.I. Publication No. 11-80647, wascoated on the resulting layer and dried.

The resist 19′ being removed with MEK, the resulting material was driedat 200° C. for 15 minutes in a nitrogen atmosphere to form an Agparticle fused layer, whereby a drain electrode 4 and a source electrode5 were formed. Each electrode was comprised of a layer of polystyrenesulfonic acid and poly(ethylenedioxythiophene) with a thickness of 20 nmand an Ag particle fused layer with a thickness of 300 nm, which wasprovided on the layer of polystyrene sulfonic acid andpoly(ethylenedioxythiophene).

(2) Preparation of Organic Thin-Film Transistor Sample 2

Organic thin-film transistor sample 2 (as shown in FIG. 5) was preparedin the same manner as the organic thin-film transistor sample 1, exceptthat neither the formation of the organic semiconductor layer protectivelayer nor the removal of the organic semiconductor layer protectivelayer was carried out. In FIG. 5, numerical numbers 1, 2, 4, 5, 6, 7, 8,and 9 are the same as those denoted in FIGS. 4(1) through 4(8).

(3) Preparation of Organic Thin-Film Transistor Sample 3

Organic thin-film transistor sample 3 (as shown in FIG. 6) was preparedin the same manner as the organic thin-film transistor sample 2, exceptthat at the formation of source electrode and drain electrode, anaqueous dispersion (BAYTRON P produced by Bayer Co., Ltd.) ofpolystyrene sulfonic acid and poly(ethylenedioxythiophene) was suppliedto the portions other than the resist 19′ through an ink jet printer,and dried at 100° C., and the resist 19′ was not removed. In FIG. 6,numerical numbers 1, 2, 4, 5, 6, 7, 8, 9, and 19′ are the same as thosedenoted in FIGS. 4(1) through 4(8).

(4) Preparation of Organic Thin-Film Transistor Sample 4

Organic thin-film transistor sample 4 was prepared in the same manner asthe organic thin-film transistor sample 1, except that steps from theformation of the organic semiconductor layer protective layer to theremoval of the organic semiconductor layer protective layer were notcarried out, and at the formation of source electrode and drainelectrode, gold was heat deposited onto the pentacene film through amask to form a gold layer with a thickness of 300 nm.

(5) Preparation of Organic Thin-Film Transistor Sample 5

On the surface of organic thin-film transistor sample 1 obtained above,a silicon oxide film with a thickness of 50 nm was formed as atransistor protective layer 20 according to the atmospheric pressureplasma method described above. Thus, organic thin-film transistor sample5 (as shown in FIG. 7) was prepared. In FIG. 7, numerical numbers 1, 2,3, 4, 5, 6, 7, 8, and 9 are the same as those denoted in FIGS. 4(1)through 4(8).

(6) Preparation of Organic Thin-Film Transistor Sample 6

Organic thin-film transistor sample 6 was prepared in the same manner asthe organic thin-film transistor sample 1, except that the organicsemiconductor layer protective layer was changed to a silicon oxide filmwith a thickness of 50 nm formed according to the atmospheric pressureplasma method described above, and an aqueous alkali solution with a pHof 13.5 was used at the removal of the silicon oxide film protectivelayer.

(7) Preparation of Organic Thin-Film Transistor Sample 7

Organic thin-film transistor sample 7 was prepared in the same manner asthe organic thin-film transistor sample 1, except that a silicon oxidefilm with a thickness of 50 nm was further formed on the polyvinylalcohol protective layer according to the atmospheric pressure plasmamethod described above, and at the removal of the protective layer, thesilicon oxide film was removed with an aqueous alkali solution with a pHof 13.5, and then the polyvinyl alcohol protective layer was removedwith water.

(8) Preparation of Organic Thin-Film Transistor Sample 8

On the surface of organic thin-film transistor sample 7 obtained above,a silicon oxide film 20 with a thickness of 50 nm was formed as atransistor protective layer according to the atmospheric pressure plasmamethod described above. Thus, organic thin-film transistor sample 8 (asshown in FIG. 8). In FIG. 8, numerical numbers 1, 2, 3, 4, 5, 6, 7, 8,and 9 are the same as those denoted in FIGS. 4(1) through 4(8).

(9) Preparation of Organic Thin-Film Transistor Sample 9

Organic thin-film transistor sample 9 was prepared in the same manner asthe organic thin-film transistor sample 1, except that at the formationof the source electrode and the drain electrode, an Au layer (10 nm), aCr layer (10 nm) and a Cu layer (20 nm) were formed in that orderaccording to a sputtering method on the entire surface of the resultingmaterial and then the resist was removed with MEK to form a sourceelectrode and a drain electrode.

(10) Preparation of Organic Thin-Film Transistor Sample 10

Organic thin-film transistor sample 10 was prepared in the same manneras the organic thin-film transistor sample 1, except that at theformation of the gate insulating layer, the resulting anodization filmwas subjected to atmospheric pressure plasma discharge treatment at 200°C. employing the following gas to obtain a 30 μm thick silicon oxidelayer, a gate insulating layer 7. (Gas used) Inert gas: helium 98.25% byvolume Reactive gas 1: an oxygen gas  1.5% by volume Reactive gas 2:tetraethoxysilane vapor  0.25% by volume (bubbled with helium gas)

Example 2

Evaluation of Organic Thin-Film Transistor Samples 1 through 10

The organic thin-film transistor sample 1 and organic thin-filmtransistor samples 5 through 10 exhibited good working property as ap-channel enhancement type FET. With respect to the organic thin-filmtransistor samples 1 through 10, carrier mobility (cm²/V·sec), and anON/OFF ratio (a drain current ratio when a drain bias was −50 V and agate bias was −50V and 0 V) were determined from a saturation region ofI-V characteristic.

Further, after the organic thin-film transistor samples 1 through 10were stored in an atmosphere for one month, the carrier mobility and theON/OFF ratio thereof were determined.

Each of the organic thin-film transistor samples 1 through 10 was foldedwhile the substrate side of each sample contacted a stainless steelshaft with an R of 10 mm, and then carrier mobility thereof wasdetermined. The results are shown in Table 1. TABLE 1 Immediately afterAfter one month After preparation storage folding Carrier CarrierCarrier Sample Mobility Mobility Mobility No. (cm²/V · sec) ON/OFF(cm²/V · sec) ON/OFF (cm²/V · sec) Remarks 1 0.2 120000 0.18 95000 0.19Inv. 2 0.003 50 0.0001 10 No working Comp. 3 0.02 120 0.018 80 0.017Comp. 4 0.15 110000 0.08 50 No working Comp. 5 0.2 120000 0.2 1200000.19 Inv. 6 0.22 120000 0.19 110000 0.2 Inv. 7 0.2 140000 0.21 1250000.2 Inv. 8 0.2 140000 0.2 130000 0.2 Inv. 9 0.2 120000 0.18 95000 0.19Inv. 10 0.2 120000 0.19 100000 0.19 Inv.Inv.: Invention,Comp.: Comparative

As is apparent from Table 1 above, inventive organic thin-filmtransistor samples provided good characteristics as transistors, andminimized deterioration with time or deterioration due to folding.

Example 3

Preparation of Organic Thin-Film Transistor Sample 11 and its Evaluation

Organic thin-film transistor sample 11 was prepared in the same manneras organic thin-film transistor sample 1, except that a mixture layer ofpolyvinyl alcohol and carbon black (=8:2 by weight) was used as anorganic semiconductor layer protective layer instead of the organicsemiconductor layer protective layer of polyvinyl alcohol. The resultingmixture layer of polyvinyl alcohol and carbon black had an average lighttransmittance at visible wavelength regions of 0.1%.

The organic thin-film transistor sample 10 provided the same good FETproperty as the organic thin-film transistor sample 1. When the sample11 immediately after prepared was exposed to light of 500 cd through atungsten lamp, properties thereof were not changed.

Example 4

Preparation of Organic Thin-Film Transistor Sample 12 and its Evaluation

Organic thin-film transistor sample 12 was prepared in the same manneras organic thin-film transistor sample 1, except that the lightsensitive layer, the source electrode and the drain electrode wereformed as follows.

The following compositions A and B individually were kneaded anddispersed employing a sand mill to obtain dispersions A and B.Subsequently, dispersion A, dispersion B, and a polyisocyanate compoundwere mixed in a ratio by weight of dispersion A: dispersion B: apolyisocyanate compound=100:2.39:0.37, and mixed with stirring in adissolver to obtain a coating liquid. The resulting coating liquid wascoated on the organic semiconductor layer protective layer 3 employingan extrusion coater, and dried at 100° C. for 5 minutes in a nitrogenatmosphere to form an ablation layer 21 {as shown in FIG. 9(1)} with athickness of 0.3 μm. In FIG. 9(1), numerical numbers 1, 2, 3, 6, 7, 8,and 9 are the same as those denoted in FIGS. 4(1) through 4(8).Composition A Fe—Al ferromagnetic metal powder 100 parts Polyurethaneresin Vylon UR-8200 10.0 parts (produced by Toyo Boseki Co., Ltd.)Polyester resin Vylon 280 5.0 parts (produced by Toyo Boseki Co., Ltd.)Phosphoric acid ester 3.0 parts Methyl ethyl ketone 105.0 parts Toluene105.0 parts Cyclohexanone 90.0 parts

Composition B α-Alumina High purity Alumina HIT60G 100 parts (Averageparticle diameter: 0.18 μm, produced by Sumitomo Kagaku Co., Ltd.)Polyurethane resin Vylon UR-8700 15 parts (produced by Toyo Boseki Co.,Ltd.) Phosphoric acid ester 3.0 parts Methyl ethyl ketone 41.3 partsToluene 41.3 parts Cyclohexanone 35.4 parts

The resulting material was exposed at an energy density of 300 mJ/cm²employing a 100 mW semiconductor laser emitting light with a wavelengthof 830 nm to ablate the ablation layer 21 at exposed portions where asource electrode and a drain electrode were to be formed, and to form aresist 21′ at portions where a source electrode and a drain electrodewere not to be formed. Further, the ablated material was sufficientlywashed with water to remove a polyvinyl alcohol protective layer atportions other than the resist (FIG. 9(2)).

An aqueous dispersion (BAYTRON P produced by Bayer Co., Ltd.) ofpolystyrene sulfonic acid and poly(ethylenedioxy-thiophene) was suppliedto portions other than the resist 21′ through an ink jet printer, anddried at 100° C. Further, an aqueous Ag particle dispersion as disclosedin Japanese Patent O.P.I. Publication No. 11-80647, was supplied toportions other than the resist through an ink jet printer, and dried toform a drain electrode 4 and a source electrode 5 (FIG. 9(3)). FIG. 9(3)corresponds to a sectional view obtained by cutting an organic thin-filmtransistor as shown in FIG. 10 with line AB. In FIG. 10, numericalnumbers 3, 4, 5 and 10 are an organic semiconductor layer protectivelayer, a source electrode, a drain electrode, and an organic thin-filmtransistor sheet, respectively.

The organic thin-film transistor sample 12 provided the same good FETproperty as the organic thin-film transistor sample 1. When the sample12 immediately after prepared was exposed to light of 500 cd through atungsten lamp, properties thereof were not changed.

EFFECT OF THE INVENTION

The present invention can provide a manufacturing method of an organicthin-film transistor minimizing deterioration of transistorcharacteristics such as deterioration with time or deterioration due tofolding, an organic thin-film transistor manufactured by themanufacturing method, and an organic thin-film transistor and an organicthin-film transistor sheet each minimizing deterioration of transistorcharacteristics such as deterioration with time or deterioration due tofolding.

1. An organic thin-film transistor comprising: a substrate; a gateelectrode formed on the substrate; a gate insulating layer formed on thesubstrate; an organic semiconductor layer protective layer with athrough hole formed on the semiconductor layer; and a source electrodeand a drain electrode, each electrode being provided so as to contactthe organic semiconductor layer through the through hole; wherein alayer formed on the organic semiconductor layer has a lighttransmittance of not more than 10%.
 2. The organic thin-film transistorof claim 1, wherein the organic semiconductor layer protective layer isformed so as to contact the organic semiconductor layer.
 3. The organicthin-film transistor of claim 1, wherein at least a part of the sourceelectrode and at least a part of the drain electrode exist in thethrough hole.
 4. The organic thin-film transistor of claim 1, whereinthe through hole has a first hole and a second hole each separated, thesource electrode being provided so as to contact the organicsemiconductor layer through the first hole, and the drain electrodebeing provided so as to contact the organic semiconductor layer throughthe second hole.
 5. The organic thin-film transistor of claim 1, whereinthe organic semiconductor layer has a light transmittance of not morethan 10%.
 6. The organic thin-film transistor of claim 1, wherein theorganic semiconductor layer protective layer is formed by coating anaqueous hydrophilic polymer solution or an aqueous hydrophilic polymerdispersion.
 7. The organic thin-film transistor of claim 1, wherein thesource electrode is formed from a conductive paste containing metalparticles, a conductive ink or a metal film precursor.
 8. The organicthin-film transistor of claim 1, wherein the drain electrode is formedfrom a conductive paste containing metal particles, a conductive ink ora metal film precursor.
 9. The organic thin-film transistor of claim 1,wherein the source electrode contains a conductive polymer.
 10. Theorganic thin-film transistor of claim 1, wherein the drain electrodecontains a conductive polymer.
 11. The organic thin-film transistor ofclaim 1, wherein the substrate is comprised of a resin.
 12. An organicthin-film transistor sheet comprising: at least two organic thin-filmtransistors comprising: a substrate; a gate electrode formed on thesubstrate; a gate insulating layer formed on the substrate; an organicsemiconductor layer protective layer with a through hole formed on thesemiconductor layer; and a source electrode and a drain electrode, eachelectrode being provided so as to contact the organic semiconductorlayer through the through hole; wherein a layer formed on the organicsemiconductor layer has a light transmittance of not more than 10%. 13.An organic thin-film transistor comprising: a substrate; a subbing layerformed on the substrate; a gate electrode formed on the subbing layer; agate insulating layer formed on the subbing layer; an organicsemiconductor layer formed on the gate insulating layer; a sourceelectrode formed on the organic semiconductor layer; a drain electrodeformed on the organic semiconductor layer; and an organic semiconductorlayer protective layer formed on the organic semiconductor layer;wherein a layer formed on the organic semiconductor layer has a lighttransmittance of not more than 10%.
 14. An organic thin-film transistorcomprising: a substrate; a subbing layer formed on the substrate; anorganic semiconductor layer formed on the subbing layer; a sourceelectrode formed on the organic semiconductor layer; a drain electrodeformed on the organic semiconductor layer; an organic semiconductorlayer protective layer formed on the organic semiconductor layer; a gateinsulating layer formed on the organic semiconductor layer protectivelayer; and a gate electrode formed on the gate insulating layer; whereina layer formed on the organic semiconductor layer has a lighttransmittance of not more than 10%.